Chemically stable anaerobic acrylic adhesive formulation

ABSTRACT

An anaerobic adhesive formulation is provided comprised of a monomeric acrylic phase consisting of 50 to 100 wt.% of one or more pluriacrylic esters and 50 to 0 wt.% of at least one unsaturated monomer chosen from the acrylic monomers and the non-acrylic unsaturated monomers and a system which produces free radicals and is inhibited in the presence of oxygen. The formulation also contains an additive for improving the impact strength and shear strength, consisting of a polyurethane performed or formed in situ and/or a heat stabilizing additive consisting of at least one epoxide resin associated with a latent hardener of said resin. The formulation is useful in anaerobic bonding.

FIELD OF THE INVENTION

The invention relates to a single-component anaerobic acrylic adhesiveformulation which is chemically stable and which is capable of producinga cured adhesive joint exhibiting improved impact and shear strengthsor/and a good thermal behaviour.

BACKGROUND OF THE INVENTION

Anaerobic acrylic adhesive formulations are mixtures based on acrylicesters capable of being polymerized by a radical route and consistingpredominantly of multiacrylic esters and chemical generators of freeradicals chosen from peroxy compounds, the said mixtures having a curewhich is inhibited by oxygen.

These anaerobic formulations remain in the uncured state as long as theyare in contact with atmospheric oxygen. On the other hand, when they areplaced between metal surfaces or other surfaces which are impervious toatmospheric oxygen, the absence of contact with oxygen leads rapidly totheir curing.

Anaerobic adhesive formulations of this kind are employed in variousfields of industry, for producing seals or assemblies and especially forlocking nuts.

Despite their growing use, anaerobic acrylic adhesive formulations stillexhibit certain disadvantages. First of all, their chemical stabilitystill remains insufficient because of the fact that, in the majority ofcases it is necessary to incorporate latent accelerators of radicalpolymerization in these formulations in order to increase the rate ofpolymerization of the acrylic monomers once the said polymerization hasbeen initiated by the free-radical generator. The presence of theseingredients in the anaerobic formulation can result in an undesirablecuring of the said formulation before its use and, for example, duringits storage. The incorporation of polymerization inhibitors, for exampleof compounds of the hydroquinone type, in the formulation reduces thisrisk of premature curing, but does not enable it to be eliminatedaltogether.

In addition, since the acrylic monomers present in the anaerobicformulations are predominantly multiacrylic esters whose polymerizationproduces a very compact polymeric network, the adhesive joints obtainedafter curing the said formulations exhibit an excessive mechanicalrigidity and hence an inadequate resistance to impact and to peelingforces. Furthermore, anaerobic adhesive formulations have a thermalstability which is not satisfactory in most cases. Finally, the saidformulations are highly fluid and this rules out the possibility ofemploying them for applications requiring the use of highly thickenedadhesive formulations, especially adhesive bonding of large flat metalsurfaces.

The objective of the invention is to provide a single-componentanaerobic acrylic adhesive formulation which makes it possible toovercome the disadvantages of the corresponding earlier formulations.

SUMMARY OF THE INVENTION

The formulation according to the invention is of the type comprising amonomeric acrylic phase consisting, by weight, of 50 to 100 % of one ormore multiacrylic esters and of 50 to 0 % of at least one unsaturatedmonomer chosen from monoacrylic monomers and nonacrylic unsaturatedmonomers capable of being polymerized by a radical route and afree-radical generating system which is soluble in the monomeric acrylicphase and whose action generating free radicals is inhibited in thepresence of oxygen, and it is characterized in that it additionallycontains, in solution in the monomeric acrylic phase, an adjuvant forimproving the impact and shear strength of the cured formulation, chosenfrom unreactive linear polyurethanes and crosslinked or uncrosslinkedpolyurethane networks formed in situ within the monomeric acrylic phasefrom a polyurethane precursor system dissolved in the said acrylic phaseand comprising one or more polyfunctional isocyanates and one or morepolyols, or/and a thermally stabilizing adjuvant consisting of at leastone epoxy resin used in combination with a latent hardener for the saidresin.

The presence, in the adhesive formulation, of the crosslinked oruncrosslinked polyurethane or of the epoxy resin used in combinationwith the latent hardener or else of both these components, leads, whenthe adhesive is curing, to the formation of an acrylic network made upof the polymer chains resulting from the polymerization of themonomer(s) of the acrylic phase, within which there are presentcrosslinked or uncrosslinked polyurethane chains or a crosslinkedpolyepoxide network, or both.

DETAILED DESCRIPTION OF THE INVENTION

The adhesive formulation in accordance with the invention exhibits anincreased chemical stability, and hence the possibility of employingmore active free-radical generating systems or else eliminating thepolymerization inhibitors which in many cases constitute a hindrance inthe envisaged applications. The presence of the polyurethane adjuvantresults in a better flexibility of the cured adhesive joint, and this isreflected in improved shear tensile, peel or impact strengths of thesaid joint, while the incorporation of the epoxy resin used incombination with the latent hardener results in a substantialimprovement in the stability of the adhesive joint at high temperatures.Lastly, the creation of the crosslinked polyurethane network in theadhesive formulation makes it possible to adjust the viscosity of thelatter as needed.

When the acrylic adhesive formulation contains only the adjuvant of thepolyurethane type, the corresponding weight percentages x of themonomeric acrylic phase and y of the polyurethane adjuvant in thecombination of both these components are advantageously such that99.8≦x≦35 and 0.2≦y≦65, and preferably such that 95≦x≦50 and 5≦y≦50.

When the acrylic adhesive formulation contains only the adjuvant of theepoxy resin type used in combination with its hardener, thecorresponding weight percentages x of the monomeric acrylic phase and zof the epoxy adjuvant in the combination of both these components areadvantageously such that 99.8≦x≦50 and 0.2≦z≦50, and preferably suchthat 95≦x≦70 and 5≦z≦30.

In the case of the adhesive formulations in accordance with theinvention including both the adjuvant of the polyurethane type and theadjuvant of the epoxy type the corresponding weight percentages x of themonomeric acrylic phase, y of the polyurethane adjuvant and z of theadjuvant of the epoxy resin type in the combination of these threecomponents of the formulation are advantageously such that 15≦x≦99.8,0.1≦y≦60 and 0.1≦z≦90 with x+y+z=100 %, and preferably such that30≦x≦89, 1≦y≦30 and 10≦z≦70 with x+y+z=100 %.

In the abovementioned formulation the percentage y represents either thepercentage of preformed linear polyurethane or the percentage of thepolyurethane precursor system.

The polyol(s) forming part of the composition of the polyurethaneprecursor system is(are) organic compounds which contain at least twohydroxyl groups in their molecules and have a number-average molecularmass of between 60 and 200,000. The said polyols may be especiallypolyetherpolyols resulting from the reaction of one or more polyols oflow molecular mass, for example ethylene glycol, propylene glycol,butylene glycol, pentylene glycol, hexylene glycol, glycerol,trimethylolpropane, trimethylolethane, pentaerythritol,dipentaerythritol, methylglycoside, sorbitol and sucrose, with one ormore epoxy compounds of the propylene oxide or ethylene oxide type orelse polyester polyols resulting from the reaction of one or moremicromolecular polyols of the abovementioned type with one or morepolycarboxylic acids such as oxalic, malonic, succinic, glutaric,adipic, pimelic, suberic, azelaic, sebacic, malic, phthalic,cyclohexanedicarboxylic or endomethylenetetrahydrophthalic acids oranhydrides of such acids. It is also possible to employ polyolscontaining nitrogen or sulphur and especially polyester amides orpolyether ester amides hydroxylated at chain ends or elsealkylenediamines or polyalkylenepolyamines in which the hydrogen atomsattached to the nitrogen atoms are replaced by hydroxyalkyl residuessuch as, for example, hydroxyethyl or hydroxypropyl.

Polyetherdiols chosen from polyoxyalkylene glycols such aspolyoxyethylene glycols, polyoxypropylene glycols, polyoxytetramethyleneglycols, polyoxypentamethylene glycols and polyoxyhexamethylene glycols,which have a number molecular mass (Mn) between 100 and 200,000, andpreferably between 200 and 50,000 are very specially suitable aspolyols, as also are aliphatic polyesterdiols such as alkylene glycol oroxyalkylene glycol polyadipates or polycaprolactones or aromaticpolyesterdiols such as the polyterephthalates of alkylene glycols or ofoxyalkylene glycols which have a number-average molecular mass ofbetween 100 and 200,000 and preferably between 200 and 50,000.

To the abovementioned diols there may also be added polyols which haveat least three hydroxyl groups in the molecule, for exampletrimethylolpropane, trimethylolethane or pentaerythritol, the saidpolyols being employed in an overall quantity representing not more than60 % and preferably between 0.5 and 15 % of the weight of the saiddiols, these polyols acting as crosslinking agents.

The polyfunctional organic isocyanates, which are employed together withthe polyols, are organic compounds containing at least two isocyanatefunctional groups in their molecule and which have a number molecularmass which is lower than 5,000. Such polyfunctional isocyanates may beacyclic or cyclic aliphatic isocyanates such as 1,6-diisocyanatohexane,isophorone diisocyanates, biuret triisocyanate, isophorone diisocyanatetrimer, dimeryl diisocyanate, diisocyanatohexane trimer,4,4,-diisocyanatodicyclohexylmethane,1,3-bis-(isocyanatomethyl)cyclohexane, the methyl ester of2,6-diisocyanatohexanoic acid or else aromati.c isocyanates such as2,4-diisocyanatotoluene, 2,6-diisocyanatotoluene,1,5-diisocyanatonaphthalene, 4,4,-diisocyanatodiphenylmethane,2,4,-diisocyanatodiphenylmethane, carbodiimidized or urethanized4,4,-diisocyanatodiphenylmethane, triisocyanatotriphenylmethane,2,4-diisocyanatotoluene trimer, 2,4-diisocyanatotoluene uretdione or2,4-diisocyanatotolunesulphonic acids or isocyanate polymers derivedfrom 4,4,-diisocyanatodiphenylmethane. The polyfunctional organicisocyanates which can be employed in accordance with the invention mayalso be chosen from isocyanate prepolymers resulting from the controlledreaction of an organic diisocyanate with a polyol, for example an adductof a diisocyanatotoluene with trimethylolpropane.

When the polyurethane adjuvant consists of an unreactive linearpolyurethane formed before its incorporation in the monomeric acrylicphase or of an uncrosslinked polyurethane formed in situ within the saidphase from the polyurethane precursor system, these polyurethanes areobtained by reaction of one or more diols with one or more difunctionalisocyanates, the said diol(s) and the said difunctional isocyanate(s)being advantageously chosen from the diols and diisocyanates referred toabove.

When the polyurethane adjuvant consists of a crosslinked polyurethaneformed in situ within the monomeric acrylic phase from the polyurethaneprecursor system, the said precursor system is made up of one or morepolyfunctional isocyanates and of one or more polyols chosen from diolsand mixtures of diols and of polyols containing at least three hydroxylfunctional groups, so that this precursor system contains a suitablequantity of at least one isocyanate containing at least three isocyanatefunctional groups or/and at least one polyol containing at least threehydroxyl functional groups, in order that crosslinking of thepolyurethane should take place without the appearance of phaseseparation. Thus, the crosslinked polyurethane precursor system can beformed by using one or more organic isocyanates consisting partly orwholly of one or more isocyanates containing at least three isocyanatefunctional groups in combination with one or more diols or with amixture of one or more diols and of one or more polyols containing atleast three hydroxyl functional groups, the quantity of the said atleast trifunctional polyol(s) representing not more than 60 %, andpreferably between 0.5 and 15 % of the overall weight of the diol(s) ofthe mixture.

The crosslinked polyurethane precursor system can also be formed byusing one or more diisocyanates in combination with a mixture of one ormore diols and of one or more polyols containing at least three hydroxylfunctional groups, the overall quantity of the said at leasttrifunctional polyol(s) representing not more than 60 % and preferablybetween 0.5 and 15 % of the overall weight of the diol(s) of themixture.

The corresponding proportions of the polyol(s) and of the polyfunctionalisocyanate(s) to be employed to constitute the polyurethane precursorsystem correspond substantially to those ensuring a stoichiometrybetween the isocyanate groups and the hydroxyl groups, it beingpreferred to employ a slight excess of the polyisocyanate(s) in relationto stoichiometry, to prevent possible interfering secondary reactionswith some acrylic monomers.

The epoxy resin present in the adhesive formulation in accordance withthe invention may consist of a single epoxy resin or of a mixture ofepoxy resins, chosen from the various known epoxy resins which containat least two epoxide groups in their molecule. Examples of epoxy resinswhich can be employed in accordance with the invehtion are those such asthe diglycidyl ether of 2,2-bis(4-hydroxyphenyl)propane, also calledbisphenol A, the diglycidyl ether of tetrabromobisphenol A, thediglycidyl ether of bis(4-hydroxyphenyl)methane, also called bisphenolF, the triglycidyl ether of trihydroxyphenylmethane, the triglycidylether of para-aminophenol, the tetraglycidyl ether ofmethylenedianiline, the tetraglycidyl ether of tetraphenylolethane, thepolyglycidyl ethers of phenol/formaldehyde resins, the polyglycidylethers of cresol/formaldehyde resins, polyepoxidized resins of theepoxyhydantoin or epoxycyanurate type, epoxidized polyoxypropylenes,glycidyl phthalates and cycloaliphatic epoxy resins.

As indicated above, the adhesive formulation contains a latent hardenerfor the epoxy resin, that is to say, according to the invention, acompound which is capable of crosslinking the epoxy resin when thetemperature within the adhesive formulation exceeds a certain threshold,in particular has a value higher than 60° C. and preferably higher than80° C., and which is substantially inactive within the composition whenthe temperature of the latter is below the said threshold. A descriptionof the epoxy resin hardeners from which the latent hardener employed inthe adhesive formulation according to the invention can be chosen isgiven, among others, in the books "Handbook of Epoxy Resins" by Lee andNeville (McGraw-Hill Publ. 1967), chapters 7 to 13 and 15-16, and "EpoxyResins Chemistry and Technology" by May and Tanaka (Dekker Publ. 1973),pages 239 to 325. The preferred hardeners in accordance with theinvention consist of aromatic diamines, especially bis(aminophenyl)sulphones such as bis(4-aminophenyl) sulphone and dicyandiamide.According to the invention, the epoxy resin hardener of the aromaticamine type may be prereacted with a part of the epoxy resin to form anadduct and the adduct thus obtained may be employed as a modifiedhardener.

The quantity of latent hardener of the aromatic diamine type present inthe formulation advantageously represents 1 to 30 %, and preferably 5 to15 %, of the weight of the epoxy resin.

To improve the activity of the abovementioned hardener, one or morecatalysts may be added to the adhesive formulation, consisting inparticular of Lewis acids, especially BF₃ and SnCl₂ or of complexes ofsuch Lewis acids with amines such as monoethylamine (abbreviated toMEA), dimethylaniline, benzylamine, piperidine, or else with ethers suchas dialkyl ethers like ethyl ether or methyl ether, or yet again withalcohols such as methanol, ethylene glycol, butylene glycol ordiethylene glycol.

These compounds of the Lewis acid type may also be employed bythemselves as hardeners for the epoxy resin, in a quantity ranging from0.5 to 10 %, and preferably from 1 to 6 %, of the weight of this resin.

The multiacrylic esters, which constitute the major fraction of themonomeric acrylic phase, are polyfunctional acrylic esters containing intheir molecule at least two groups of formula ##STR1## in which Rdenotes a hydrogen or chlorine atom or a C₁ -C₃ alkyl radical,especially methyl.

Advantageously, the said multiacrylic esters correspond to the formula##STR2## in which A denotes an m-valent organic radical containing from2 to 50 carbon atoms, R has the abovementioned meaning and m is aninteger equal to at least 2, and preferably ranging from 2 to 5.

In particular, the multiacrylic monomers may be chosen from:

the polyacrylic esters of polyols, which include especially alkylenediacrylates and dimethacrylates such as tetramethylene or hexamethylenediacrylates and dimethacrylates, polyoxyalkylene diacrylates anddimethacrylates such as diethylene glycol, triethylene glycol,tetraethylene glycol or dipropylene glycol diacrylates ordimethacrylates, triacrylates and trimethacrylates such astrimethylolpropane triacrylate or trimethacrylate, tetracrylates andtetramethacrylates such as diglycerol tetracrylate andtetramet.hacrylate or pentaerythritol tetracrylate andtetramethacrylate, and pentacrylates and pentamethacrylates such asthose of pentaerythritolmonohydroxy;

prepolymer esters containing acrylic end groups prepared by treatingwith a hydroxyalkyl or aminoalkyl acrylate or methacrylate the reactionproduction of an excess of an isocyanate with a polyamine containingprimary or secondary amine groups or a polyol; and

monomers of the urethane/acrylate or ureide/acrylate type, resultingfrom the reaction of a polyisocyanate with an acrylic ester such as anacrylate or a methacrylate in which the ester residue contains ahydroxyl group or a primary or secondary amine group.

The preferred multiacrylic esters are the diacrylic esters correspondingto the formula ##STR3## in which R is a hydrogen atom or a methylradical, n is an integer ranging from 2 to 4 and preferably equal to 2or 3, and p is an integer ranging from 2 to 12 and preferably taking thevalues from 2 to 8.

Examples of such esters are those such as triethylene glycol,tetraethylene glycol, pentamethylene glycol, hexamethylene glycol ordipropylene glycol diacrylates and dimethacrylates.

The monoacrylic monomers and the nonacrylic unsaturated monomers capableof being polymerized by a radical route which are capable of being usedin combination with the multiacrylic esters must be compatible with themultiacrylic esters, that is to say miscible with the said esters, toform a homogeneous monomeric acrylic phase.

The monoacrylic monomers are, in particular, chosen from acryliccompounds of formula ##STR4## in which R₂ denotes a hydrogen atom or aC₁ -C₃ alkyl radical and Y denotes a nitrile group or ##STR5## residuewith R₃ denoting a radical chosen from monovalent radicals containing upto 12 carbon atoms and especially from C₁ -C₁₂ alkyl, aminoalkyl,epoxyalkyl, hydroxyalkyl and chloroalkyl radicals, C₄ -C₁₂ cycloalkyl orheterocyclic radicals and C₂ -C₁₂ alkenyl radicals. Examples of thesemonomers are those such as isobutyl methacrylate, hexyl methacrylate,lauryl methacrylate, ethyl acrylate, isobutyl acrylate, 2-ethylhexylacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate,glycidyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate,acrylonitrile and methacrylonitrile.

Compounds such as, in particular, styrene, alpha-methylstyrene, indene,divinylbenzene, vinylpyrrolidone and vinyl acetate may be mentionedamong the nonacrylic unsaturated monomers.

When the monomeric acrylic phase contains one or more nonacrylicunsaturated monomers capable of being polymerized by a radical route,the overall proportion of the said unsaturated monomers in the saidphase is preferably equal to at most 20 % of the overall weight of thevarious monomers which it contains.

Advantageously, the free-radical generating system consists of at leastone peroxy compound which is soluble in the monomeric acrylic phase andwhose free-radical generating action is inhibited by oxygen, or of acombination of a peroxy compound of this kind with one or moreactivators. The peroxy compound(s) of the free-radical generating systemmay consist especially of peroxides such as dialkyl peroxides, forexample di-tert-butyl peroxides, dicumyl peroxides, lauroyl peroxide ormore especially of hydroperoxides and of peroxy compounds capable ofdecomposing or hydrolysing to give hydroperoxides in situ. The peroxycompound of the free-radical generating system is preferably made up ofone or more organic hydroperoxides corresponding to the formula R₄ OOH,in which R. denotes a C₂ -C₁₈ and preferably C₃ -C₁₂ hydrocarbonradical, the said radical being optionally substituted by one or morefunctional groups without action on the hydroperoxide functional group,the radical R₄ being in particular an alkyl, aryl or aralkyl radical.Examples of such organic hydroperoxides are those such as cumenehydroperoxide, tert-butyl hydroperoxide, methyl ethyl ketonehydroperoxide, isopropyl hydroperoxide and cyclohexyl hydroperoxide.

In some cases it may be advantageous to employ hydroperoxides incombination with other peroxy compounds and especially with peroxidessuch as dialkyl peroxides.

The quantity of the free-radical generating system in the anaerobicadhesive formulation may vary quite widely depending on the nature ofthe said system and that of the monomers to be polymerized. When thefree-radical generating system consists of one or more peroxy compoundsor contains one or more of the said compounds, the total quantity ofperoxy compounds in this system is less than 10 % and is preferablysituated between 0.1 and 6 % of the weight of the monomers to bepolymerized which are present in the formulation.

The activators capable of being used in combination with the peroxycompounds to form the free-radical generating system are especiallytertiary amines in which the radicals attached to the nitrogen atomcontain up to ten carbon atoms each and, in particular, trialkylaminessuch as triethylamine or tributylamine, or else N,N-dialkylarylaminessuch as N,N-dimethyl-para-toluidine, or else heterocyclic secondaryamines, for example pyrrolidine, piperazine and1,2,3,4-tetrahydroquinoline, or else organic sulphimides and, forexample, saccharin, which are employed by themselves or in combinationwith heterocyclic secondary amines or N,N-dialkylarylamines, or elsecompounds such as succinimide, phthalimide and formamide. The quantityof activator may vary within wide limits. The total quantity ofactivator is advantageously less than 10 % and preferably between 0.05 %and 6 % of the weight of the monomers to be polymerized which arepresent in the anaerobic formulation.

Although the formulation in accordance with the invention exhibits goodchemical stability, this stability can be improved further byincorporating polymerization inhibitors in the said formulation and, inparticular, phenolic compounds such as 2,6-ditert-butyl-4-methylphenol,or else quinones or hydroquinones, in a quantity representing, forexample, 10 to 10,000 ppm, and preferably 10 to 5,000 ppm.

To prevent the detrimental influence of metallic impurities which may bepresent in the ingredients making up the formulation or introducedduring the preparation of the formulation in metallic mixing devices, onthe storage stability of the anaerobic formulation, chelating agentscapable of complexing the said metallic impurities may also be added toit. Chelating agents which are particularly suitable areα-aminocarboxylates or aminocarboxylates such as the alkali metal saltsof alkylenediaminetetracetic acids and especially the tetrasodium saltof ethylenediaminetetracetic acid, β-substituted hydroxyaryl compoundssuch as salicylaldehyde, orthoaminophenol, the disodium salt ofpyrocatechol and the disodium salt of ortho-thiobenzoic acid, or elsecompounds such as bipyridyl, tripyridyl, 8-hydroxyquinoline,1,10-phenanthroline and salicylaldoxime. The chelating agent isincorporated in the anaerobic formulation in a proportion of 10 to 3,000ppm and preferably 50 to 1,000 ppm.

If need be, other ingredients capable of imparting desirable additionalproperties to the anaerobic adhesive formulation may also beincorporated in the said formulation, it being possible for suchingredients to include especially thickeners, plasticizers, colorants orthixotropic agents. The said ingredients are employed in quantitiescorresponding to those generally recommended in the art.

The anaerobic formulation in accordance with the invention alwayscontains a certain quantity of dissolved oxygen and it is preferablysaturated with oxygen.

The anaerobic formulation can be prepared by any mixing method whichmakes it possible to produce a homogeneous and stable mixture of theingredients forming part of the composition of the said formulation.

The anaerobic adhesive formulation in accordance with the invention canbe employed in the various applications of conventional anaerobicformulations. It may be employed, for example, for the production ofassemblies and in particular for locking nuts or else for producingseals, or even for performing structural adhesive bonding by first ofall producing a partial curing of the adhesive joint at an ambient orslightly elevated temperature, and then subjecting the partially curedadhesive joint to a postcure at a higher temperature.

The invention is illustrated by the following examples, which are givenwithout any limitation being implied:

EXAMPLE 1

Six anaerobic adhesive formulations were prepared, whose compositionsare given in parts by weight in Table I. One of the formulations, namelyformulation A is a control formulation, while the others (formulations1.1 to 1.5) are formulations in accordance with the invention.

                  TABLE I                                                         ______________________________________                                               Formulation                                                                     A     1.1     1.2     1.3   1.4   1.5                                ______________________________________                                        Triethylene                                                                             97      87.3    77.6  67.9  58.2  48.5                              glycol                                                                        dimeth-                                                                       acrylate                                                                      Linear     0      10      20    30    40    50                                polyure-                                                                      thane α)                                                                CHP β)                                                                              3       2.7     2.4   2.2   1.8   1.5                              Saccharin                                                                                0.3     0.27    0.24                                                                                0.21                                                                                0.18                                                                                0.15                             N,N-Dimeth-                                                                              0.3     0.27    0.24                                                                                0.21                                                                                0.18                                                                                0.15                             yl-para-                                                                      toluidine                                                                     Hydroqui-                                                                              1000    1000    1000  1000  1000  1000                               none                                                                          (ppm) γ)                                                                ______________________________________                                         α)  Unreactive linear polyurethane prepared by polycondensation of      91.7 parts by weight of a polyetherdiol known under the name of P2000 and     consisting of a polyoxypropylene glycol of Mn equal to 2000 with 8.3 part     by weight of toluene diisocyanate, the polyurethane formed being separate     from the reaction mixture by precipitation.                                   β)  CHP: cumene hydroperoxide                                            γ)  The quantity of hydroquinone is expressed in ppm by weight          relative to the total of the other ingredients of the formulation.       

Preparation of the Control Formulation

First of all, air was bubbled through the dimethacrylate for one hour atambient temperature and then, while the bubbling was continued and theoperation was carried out with mechanical stirring at ambienttemperature, the saccharin, N,N-dimethyl-para-toluidine, CHP and lastlyhydroquinone were dissolved successively in the dimethacrylate, thehydroquinone being added in the form of a 10% solution in methanol.

Preparation of the Formulations in Accordance with the Invention

First of all, air was bubbled through the dimethacrylate for one hour atambient temperature and then, while the air bubbling was continued andthe operation was carried out with mechanical stirring, the linearpolyurethane was first of all dissolved in the dimethacrylate at atemperature of about 50° C., followed successively at ambienttemperature by the saccharin, N,N-dimethyl-para-toluidine, and CHP andlastly hydroquinone, the latter being added as a 10 % solution inmethanol.

The adhesive formulations thus obtained were then subjected to varioustests to determine the viscosity, the gel time and the setting time ofeach of the said formulations.

Determination of the Gel Time

In this test, a volume of adhesive formulation equal to 2 cm³ was placedin a test tube 125 mm in length and 15 mm in diameter. The tube was thenclosed and placed in a bath maintained at a constant temperature of 80°C. The time elapsed between the instant when the test tube is placed inthe bath and the instant when a beginning of gelling of the formulationcontained in the tube is observed was noted and this time was taken as ameasurement of the gel time, the said time giving a measurement of thestability of the formulation. A high gel time corresponds to a highstability of the adhesive formulation.

Determination of the Setting Time

In this test, several drops of the anaerobic formulation were placed onthe threads of a steel bolt with an external thread diameter of 9.52 mmand comprising 24 threads per 2.54 cm, and of the corresponding nut, andthese components were then assembled. The nut was moved slightlyrelative to the bolt at regular intervals to determine the instant whenthe polymerization took place. When it was no longer possible to rotatethe nut by hand relative to the bolt, the total elapsed time was notedand this time was taken as a measurement of the setting time. This timeis proportionally shorter the higher the rate of curing of the anaerobicformulation.

The anaerobic adhesive formulations were also employed to carry out, onthe one hand, nut unlocking tests and, on the other hand, tests foradhesive bonding of steel sterigmata to evaluate the strength of thecured adhesive joint.

Nut Unlocking Test

A steel bolt with an external thread diameter of 9.52 mm and comprising24 threads per 2.54 cm of length, and the corresponding nut, wereemployed. A few drops of the anaerobic formulation were placed on thethreads of the bolt and of the nut and the said components were thenassembled while ensuring that a sufficient quantity of liquid waspresent in the threads to produce a good seal. The bolt/nut assemblieswere then subjected to a thermal treatment so as to cause the adhesiveto cure.

At the end of the thermal treatment, the unlocking torque of the nut wasmeasured by using a torque key.

Test on Adhesive Bonding of Steel Sterigmata

Assemblies consisting of two steel sterigmata were produced, each being10 cm in length, 2.5 cm in width and 0.4 cm in thickness, these beingadhesively bonded to each other by means of the chosen anaerobicformulation. To produce the said assemblies, one of the faces of a firststerigma, degreased with trichloroethylene, beforehand, was coated witha uniform layer of the anaerobic formulation and the face of a secondsterigma, also degreased with trichloroethylene, was then applied ontothe face of the first sterigma coated in this way, so as to form anassembly comprising an adhesive joint approximately 1.25 cm in length.

The assemblies obtained were then subjected to a thermal treatment,after which the shear strength of the adhesive joint was determined bysubjecting the assemblies to a shear tensile test by following thespecifications of ASTM standard D 1002-72. To carry out the sheartensile test, the speed of travel of the jaws of the tensometer wasequal to 1.33 mm/minute.

The values of the various quantities measured are given in Table II,each representing an average value determined over ten tests.

On inspecting the results which appear in Table II it can be seen thatthe addition of an unreactive linear polyurethane to an anaerobicacrylic formulation makes it possible to vary the value of the unlockingtorque of the bolt/nut assemblies. In addition, the shear strength ofthe cured adhesive joints containing a polyurethane of this kind isimproved in the majority of cases, compared with that of the control.

                  TABLE II                                                        ______________________________________                                                   Formulation                                                                   A     1.1     1.2    1.3  1.4  1.5                                 ______________________________________                                        Viscosity at 10 s.sup.-1                                                                   0.008   0.073   0.29 0.68 1.12 1.17                              (Pa s)                                                                        Gel time at 80° C.                                                                  15      7       10   15   45   40                                (min)                                                                         Setting time (min)                                                                         25      25      25   25   45   60                                Unlocking torque                                                              after thermal                                                                 treatment (N m)                                                               24 h at ambient                                                                            13      24      20   15   11   2                                 24 h at ambient +                                                                          29      25      17   15   12   8                                  1 h at 80° C.                                                          1 h at 80° C. +                                                                    30      25      20   16   12   8                                  1 h at 150° C.                                                         1 h at 80° C. +                                                                    29      18      13   6    5    6                                  1 h at 220° C.                                                        Shear strength after                                                          thermal treatment                                                             (MPa)                                                                         24 h at ambient                                                                            1.7     1.6     2.6  2    0.6  0                                 24 h at ambient +                                                                          1.9     1.5     2.2  3.1  2.6  1.9                                1 h at 80° C.                                                          1 h at 80° C. +                                                                    2.3     1       6    4.5  3.6  3.3                                1 h at 150° C.                                                         1 h at 80° C. +                                                                    1       2.3     1.5  2.2  0.7  0.9                                1 h at 220° C.                                                        ______________________________________                                    

EXAMPLE 2

Six anaerobic adhesive formulations were prepared, whose compositionsare given in parts by weight in Table III. One of the formulations,namely formulation A is the control formulation whose preparation isgiven in Example 1, while the others (formulations 2.1 to 2.5) areformulations in accordance with the invention.

                  TABLE III                                                       ______________________________________                                               Formulation                                                                     A     2.1     2.2     2.3   2.4   2.5                                ______________________________________                                        Triethylene                                                                             97      87.3    77.6  67.9  58.2  48.5                              glycol                                                                        dimethacry-                                                                   late                                                                          Polyurethane                                                                  precursors                                                                    Polyetherdiol                                                                            0       7.75   15.5  23.25                                                                               31    38.75                             P2000                                                                         Polyfunc-                                                                                0       2.95    5.9   8.85                                                                                11.8                                                                               14.75                             tional                                                                        isocyanate δ)                                                           CHP        3       2.7     2.4   2.1   1.8   1.5                              Saccharin                                                                                0.3     0.27    0.24                                                                                0.21                                                                                0.18                                                                                0.15                             N,N-Dimeth-                                                                              0.3     0.27    0.24                                                                                0.21                                                                                0.18                                                                                0.15                             yl-para-                                                                      toluidine                                                                     Hydroqui-                                                                              1000    1000    1000  1000  1000  1000                               none                                                                          (ppm)                                                                         ______________________________________                                         δ): Adduct of toluene diisocyanate and of trimethylolpropane            marketed by Bayer under the name Desmodur L 75.                          

Preparation of the Formulations in Accordance with the Invention

First of all, air was bubbled through the dimethacrylate for one hour atambient temperature and then, while the air bubbling was maintained andthe mixture was stirred mechanically, the polyetherdiol and thepolyfunctional isocyanate were successively added to the dimethacrylateand the whoel was homogeneized for 2 hours at ambient temperature andthe homogenized mixture was then heated to 60° C. and this temperaturewas maintained for one hour to improve the formation of the polyurethanein situ. The saccharin, N,N-dimethyl-para-toluidine and CHP were thensuccessively added at ambient temperature to the mixture thus obtained,followed by the hydroquinone, the latter being employed as a 10 %solution in methanol.

The adhesive formulations prepared were then subjected to various tests,as shown in Example 1 to determine the viscosity, the gel time and thesetting time of the said formulations, together with the values of theunlocking torque and the shear strength of the cured adhesive joint.

The values of the various quantities measured are given in Table IV,each representing an average value over ten tests.

From an inspection of the results shown in Table IV it follows that theformation of the polyurethane within the adhesive formulation yieldsformulations which are more fluid than the formulations containing apreformed polyurethane and have a slightly longer gel time, togetherwith higher values of the unlocking torque and of the shear strength.

                  TABLE IV                                                        ______________________________________                                                 Formulation                                                                   A     2.1    2.2     2.3   2.4   2.5                                 ______________________________________                                        Viscosity at                                                                             0.009   0.02   0.032 0.036 0.051 0.27                              10 s.sup.-1 (Pa s)                                                            Gel time at 80° C.                                                                15      20     15    45    60    80                                (min)                                                                         Setting time (min)                                                                       25      25     25    25    15    50                                Unlocking torque                                                              after thermal                                                                 treatment (N m)                                                               24 h at ambient                                                                          13      32     18    18    13    7                                 24 h at ambient +                                                                        29      30     18    25    11    7                                  1 h at 80° C.                                                          1 h at 80° C. +                                                                  30      42     17    24    10    6                                  1 h at 150° C.                                                         1 h at 80° C. +                                                                  29      18     16    17    6     4                                  1 h at 220° C.                                                        Shear strength                                                                after thermal                                                                 treatment (MPa)                                                               24 h at ambient                                                                          1.7     3      2.3   0.6                                           24 h at ambient +                                                                        1.9     1.7    4.1   3.7   1.9   0.8                                1 h at 80° C.                                                          1 h at 80° C. +                                                                  2.3     1.3    5.6   4.9   1.7   0.8                                1 h at 150° C.                                                         1 h at 80° C. +                                                                  1       1.2    3.5   5     1     0.5                                1 h at 220° C.                                                        ______________________________________                                    

EXAMPLE 3

By operating in a manner similar to that described in Example 2, threeanaerobic adhesive formulations in accordance with the invention wereprepared, namely formulations 3.1 to 3.3, whose compositions are thoseof formulations 2.1 to 2.3 respectively, except that the formulations3.1 to 3.3 are free from saccharin, N,N-dimethyl-para-toluidine andhydroquinone.

Using the anaerobic adhesive formulations thus obtained and operating asshown in Example 1, assemblies were formed from steel sterigmata and thesaid assemblies were subjected to a thermal treatment and then to ashear tensile test to determine the shear strength of the adhesivejoint.

Formulation 3.2 was also employed for a test to determine the nutunlocking torque after thermal treatment as shown in Example 1.

The results obtained are assembled in Table V.

                  TABLE V                                                         ______________________________________                                                       Formulation                                                                   3.1     3.2    3.3                                             ______________________________________                                        Shear strength after                                                          thermal treatment (MPa)                                                       24 h at ambient  4.2       4.9    4.5                                         24 h at ambient +                                                                              4.2       7.9    7.8                                          1 h at 80° C.                                                          1 h at 80° C. +                                                                        9.6       13.4   13                                           1 h at 150° C.                                                        Unlocking torque after                                                        thermal treatment (N m)                                                       24 h at ambient            20                                                 24 h at ambient +          20                                                  1 h at 80° C.                                                          1 h at 80° C. +    26                                                  1 h at 150° C.                                                        ______________________________________                                    

EXAMPLE 4

By operating in a manner similar to that described in Example 2, threeanaerobic adhesive formulations in accordance with the invention wereprepared, namely formulations 4.1 to 4.3, whose compositions are thoseof formulations 2.1 to 2.3 respectively, except that formulations 4.1to 4.3 contained only 200 ppm of hydroquinone and that thedimethacrylate employed was tetraethylene glycol dimethacrylate.

The adhesive formulations thus obtained were subjected to tests asindicated in Example 1, to determine the gel time and the setting timeof each of the said formulatiosn and also to the test to determine theunlocking torque of bolt/nut systems assembled by means of theseformulations.

The results obtained, which are averages over ten tests, are assembledin Table VI.

On comapring the results shown in Tables IV and VI it cna be seen thattetraethylene glycol dimethacrylate gives anaerobic adhesiveformulatiosn which are chemically more stable and more advantageous withregard to mechanical properties than those making use of triethyleneglycol dimethacrylate.

                  TABLE VI                                                        ______________________________________                                                      Formulation                                                                   4.1       4.2   4.3                                             ______________________________________                                        Gel time at 80° C. (min)                                                               25          50    65                                          Setting time (min)                                                                            10          12    13                                          Unlocking torque after                                                        thermal treatment (N m)                                                       24 h at ambient 33          23    25                                          24 h at ambient +                                                                             40          28                                                 1 h at 80° C.                                                          1 h at 80° C. +                                                                       35          23                                                 1 h at 150° C.                                                         1 h at 80° C. +                                                                       18          21                                                 1 h at 220° C.                                                        ______________________________________                                    

EXAMPLE 5

Three anaerobic adhesive formulations in accordance with the inventionwere prepared, namely formualtions 5.1 to 5.3, whose compositions inparts by weight are given in Table VII.

                  TABLE VII                                                       ______________________________________                                                      Formulation                                                                   5.1     5.2     5.3                                             ______________________________________                                        Triethylene glycol                                                                            87.3      77.6    87.3                                        dimethacrylate                                                                CHP             2.7       2.4     2.7                                         Saccharin       0.27      0.24    0.27                                        N,N-Dimethyl-para-                                                                            0.27      0.24    0.27                                        toluidine                                                                     Epoxy resin (BADGE).sup.ε)                                                            10        20      10                                          Bis(4-aminophenyl)                                                                            1         2       1                                           sulphone                                                                      BF.sub.3.MEA.sup.λ)                                                                    0.01      0.02    0.01                                        Hydroquinone (ppm)                                                                            200       200     1000                                        ______________________________________                                         .sup.ε)  BADGE = bisphenol A diglycidyl ether                         .sup.λ)  BF.sub.3.MEA = BF.sub.3monoethylamine complex            

Preparation of the Adhesive Formulatsion

First of all, a solution of bis(4-aminophenyl) sulphone, abbreviated toDDS, and of the BF₃.MEA complex in the epoxy resin was prepared. To dothis, DDS was dissolved in the epoxy resin, kept stirred at atemperature of approximately 110° C., and the solution thus obtained wasthen cooled to approximately 85° C. and the BF₃.MEA complex was thenincorporated in it.

Separately, air was bubbled through the dimethacrylate for one hour atambient temperature and then, while the air bubbling was continued andthe mixture was stirred mechanically, the temperature of the latter wasraised to approximately 65° C. and while the said temperature wasmaintained the epoxy resin containing DDS and the BF₃.MEA complex insolution was incorporated in it. The solution formed was then cooled toa temperature close to the ambient and the saccharin,N,N-dimethyl-para-toluidine and CHP were then successively incorporatedin it with stirring and bubbling of air, followed by the hydroquinone inthe form of a 10 % solution in methanol.

The anaerobic adhesive formulations thus obtained were subjected totests, as shown in Example 1, to determine the gel time and the settingtime of each of the said formulations and, furthermore, the unlockingtorque of bolt/nut systems assembled by means of these formulations,together with the shear strength of the cured adhesive joint afterthermal treatment.

The results obtained, which represent averages over ten tests, arelisted in Table VIII.

                  TABLE VIII                                                      ______________________________________                                                       Formulation                                                                   5.1     5.2     5.3                                            ______________________________________                                        Gel time                                                                      at 80° C. 6 min     7 min   30 min.                                    at 25° C. several   several several                                                     months    months  months                                     Setting time (min)                                                                             5         8       25                                         Unlocking torque after                                                        thermal treatment (N m)                                                       24 h at ambient  40        28                                                 24 h at ambient +                                                                              38        30                                                  1 h at 80° C.                                                          1 h at 80° C. +                                                                        42        32                                                  1 h at 150° C.                                                         1 h at 80° C. +                                                                        54.5      45                                                  1 h at 220° C.                                                        Shear strength after                                                          thermal treatment (MPa)                                                       24 h at ambient  2.2       1.7                                                24 h at ambient +                                                                              1.6       1.6                                                 1 h at 80° C.                                                          1 h at 80° C. +                                                                        2.2       2.3                                                 1 h at 150° C.                                                         1 h at 80° C. +                                                                        4.7       3.7                                                 1 h at 220° C.                                                        ______________________________________                                    

Comparison of the results of Table VIII with those obtained with thecontrol formulation A shows that the creation of a three-dimensionalpolyepoxide network within the acrylic adhesive joint results in highervalues of the unlocking torque and in an improved thermal stability ofthe cured adhesive joint.

EXAMPLE 6

Four anaerobic adhesive formulations in accordance with the inventionwere prepared, namely formulations 6.1 to 6.4, whose compositions inparts by weight are given in Table IX.

                  TABLE IX                                                        ______________________________________                                                     Formulation                                                                   6.1   6.2      6.3     6.4                                       ______________________________________                                        Triethylene glycol                                                                           48.5    58.2     72.2  63.05                                   dimethacrylate                                                                Polyurethane precursors                                                       Polyetherdiol P2000                                                                          7.75    12.9     5.8   11.6                                    Desmodur L 75  2.95    2.95     2.2   4.4                                     isocyanate                                                                    CHP            1.5     1.8      2.25  1.95                                    Saccharin      0.15    0.18     0.225 0.195                                   N,N-Dimethyl-para-                                                                           0.15    0.18     0.225 0.195                                   toluidine                                                                     Epoxy resin (BADGE)                                                                          40      30       17.5  20                                      DDS            4       3        1.75  2                                       BF.sub.3.MEA   0.4     0.3      0.175 0.2                                     Hydroquinone (ppm)                                                                           200     200                                                    ______________________________________                                    

Preparation of the Adhesive Formulations

First of all, a solution of DDS and of the BF₃.MEA complex in the epoxyresin was prepared as shown in Example 5.

Separately, air was bubbled through the dimethacrylate for one hour atambient temperature and then, while the air bubbling was continued andthe mixture was stirred mechanically, the polyetherdiol was added to thedimethacrylate, followed by the isocyanate, and the whole washomogenized for 2 hours at ambient temperature and the homogenizedmixture was then heated to approximately 65° C. and this temperature wasmaintained for one hour to improve the formation of the polyurethanenetwork in situ. The epoxy resin containing the DDS and the BF₃.MEAcomplex in solution incorporated in the mixture obtained, stillmaintained at a temperature of approximately 65° C. and with stirringand bubbling of air. The mixture thus produced was then returned toambient temperature and the saccharin, N,N-dimethyl-para-toluidine andCHP were then successively added to it, followed by the hydroquinone asa 10 % solution in methanol.

The anaerobic formulations thus prepared were subjected to tests, asshown in Example 1, to determine the gel time and the setting time ofeach of the said formulations and, furthermore, the unlocking torque ofbolt/nut systems assembled by means of these formulations, together withthe shear strength of the cured adhesive joint after thermal treatment.

The results obtained, which are averages over ten tests, are assembledin Table X.

                  TABLE X                                                         ______________________________________                                                       Formulation                                                                   6.1   6.2     6.3     6.4                                      ______________________________________                                        Gel time at 80° C. (min)                                                                240     180     180   180                                    Setting time (min)                                                                             90      45      13    23                                     Unlocking torque after                                                        thermal treatment (N m)                                                       24 h at ambient  12      22      30    23                                     24 h at ambient + 1 h at 80° C.                                                         15      30      38    28                                      1 h at 80° C. + 1 h at 150° C.                                                  35      33      41    40                                      1 h at 80° C. + 1 h at 220° C.                                                  51      42      49    43                                     Shear strength after                                                          thermal treatment (MPa)                                                       24 h at ambient  1.8     2.9     3.8   5.6                                    24 h at ambient + 1 h at 80° C.                                                         5.3     5.5     3.1   6.8                                     1 h at 80° C. + 1 h at 150° C.                                                  12.7    8       2.6   7.8                                     1 h at 80° C. + 1 h at 220° C.                                                  16      7.5     2.5   5.1                                    ______________________________________                                    

On inspecting the results in Table X it appears that the creation of apolyurethane network and of a three-dimensional polyepoxide networkwithin the acrylic joint makes it possible not only to obtain anadhesive joint exhibiting good thermal stability, but also to expectgood mechanical performance in respect of thread locking and at the sametime, in some cases (formulation 6.1), with regard to the assemblies ofstructural elements.

EXAMPLE 7

Formulations 6.1 and 6.3 were evaluated again after being kept for 15days in the dark to determine the influence of ageing on the saidformulations.

The results of nut unlocking and shear tensile tests performed with theuse of the aged formulations are given in Table XI.

The results listed in Table XI demonstrate that the formulations havenot changed with respect to the crosslinking and that, in addition,there is a significant improvement in the mechanical characteristics ofthe adhesive joints resulting from the aged formulations.

                  TABLE XI                                                        ______________________________________                                                           Formulation                                                                   6.1  6.3                                                                      aged aged                                                  ______________________________________                                        Unlocking torque after                                                        thermal treatment (N m)                                                       24 h at ambient      8      18.7                                              24 h at ambient +    18     40                                                 1 h at 80° C.                                                          1 h at 80° C. +                                                                            70     44                                                 1 h at 150° C.                                                         1 h at 80° C. +                                                                            67     54                                                 1 h at 220° C.                                                        Shear strength after                                                          thermal treatment (MPa)                                                       24 h at ambient      1      1.9                                               24 h at ambient +    5.9    3.2                                                1 h at 80° C.                                                          1 h at 80° C. +                                                                            14     14                                                 1 h at 150° C.                                                         1 h at 80° C. +                                                                            16     15.5                                               1 h at 220° C.                                                        ______________________________________                                    

EXAMPLE 8

By operating in a manner similar to that described in Example 6, ananaerobic adhesive formulation in accordance with the invention wasprepared, namely formulation 8.1, whose composition corresponded to thatof formulation 6.1, except that formulation 8.1 did not containhydroquinone.

The adhesive formulation thus obtained was subjected to tests, as shownin Example 1, to determine, on the one hand, the gel time and thesetting time of the formulation and, on the other hand, the unlockingtorque of bolt/nut systems assembled by means of this formulation,together with the shear strength of the adhesive joint after thermaltreatment.

The results obtained, which represent averages over ten tests, are givenin Table XII.

                  TABLE XII                                                       ______________________________________                                                                 Formu-                                                                        lation                                                                        8.1                                                  ______________________________________                                        Gel time at 80° C. (min)                                                                          240                                                Setting time (min)         40                                                 Unlocking torque after thermal treatment (N m)                                24 h at ambient            12                                                 24 h at ambient + 1 h at 80° C.                                                                   18                                                  1 h at 80° C. + 1 h at 150° C.                                                            27                                                  1 h at 80° C. + 1 h at 220° C.                                                            46                                                 Shear strength after thermal treatment (MPa)                                  24 h at ambient            3.7                                                24 h at ambient + 1 h at 80° C.                                                                   5.2                                                 1 h at 80° C. + 1 h at 150° C.                                                            8                                                   1 h at 80° C. + 1 h at 220° C.                                                            10                                                 ______________________________________                                    

I claim:
 1. A single component anaerobic acrylic adhesive formulation,which is chemically stable and capable of producing a cured adhesivejoint exhibiting improved imapct and shear strengths and a good thermalbahvior, said formulation comprising:(a) a monomeric acrylic phasecomprising, by weight, 50 to 100% of at least one multiacrylic esterselected from the group consisting of polyfunctional acrylic esterscontaining at least two groups of the formula ##STR6## wherein R is ahydrogen or chlorine atom or a C₁ -C₃ alkyl radical, and 50 to 0% of atleast one unsaturated monomer selected from the group consisting ofmonacrylic monomers and non-acrylic unsaturated monomers capable ofbeing polymerized by a radical route, (b) a free radical generatingsystem which is soluble in the monomeric acrylic phase and whose actiongenerating free radicals is inhibited in the presence of oxygen, (c) anadjuvant for improving the impact and shear strength of the curedformulation, said adjuvant being in solution in the monomeric acrylicphase and consisting of a cross-linked polyurethane network formed insitu within the monomeric acrylic phase from a polyurethane precursorsystem made up of one or more organic polyfunctional isocyanates and ofone or more polyols selected from the groups consisting of diols andmixtures of diols and of polyols containing at least three hydroxylfunctional groups, wherein the precursor system contains at least oneisocyanate containing at least three isocyanate functional groups or atleast one polyol containing at least three hydroxy functional groups ora mixture thereof in an amount so sleected that cross-linking of thepolyurethane takes place without the appearance of phase separation inthe formulation, (d) a thermally stabile adjuvant soluble in themonomeric acrylic phase and consisting of one or more epoxy resinscontaining at least two epoxy groups, and (e) a latent hardener for saidresin or resins which is soluble in the monomeric acrylic phase.
 2. Theadhesive formulation according to claim 1, wherein the polyols formingpart of the polyurethane precursor system have number-average molecularweights of between 60 and 200,000.
 3. The adhesive formulation accordingto claim 1, wherein the polyfunctional isocyanates used in combinationwith he polyols to form the polyurethane precursor system have amolecular weight of less than 5,000.
 4. The adhesive formulationaccording to claim 3, wherein said polyfunctional isocyanates areselected from the group consisting of acyclic aliphatic isocyanates,cyclic aliphatic isocyanates and aromatic isocyanates.
 5. The adhesiveformulation according to claim 1, wherein the quantity of said at leastone polyol containing at least three hydroxy functional groups in thepolyurethane precursor system represents not more than 60% of the weightof the diols present in said system.
 6. The adhesive formulationaccording to claim 5, wherein said quantity is between 0.5 and 15% ofthe weight of the diols present in the polyurethane precursor system. 7.The adhesive formulation according to claim 1, wherein the diols presentin the polyurethane precursor system are selected from the groupconsisting of polyetherdiols and polyesterdiols having number-averagemoelcular weights between 100 and 200,000.
 8. The adhesive formulationaccording to claim 7, wherein said diols have number-average molecularweights between 200 and 50,000.
 9. The adhesive formulation according toclaim 1, wherein the weight percentages x of the monomeric acrylicphase, y of the polyurethane adjuvant, and z of the adjuvant of theepoxy resin type are such that 15≦x≦99.8, 0.1≦y≦60, and 0.1≦z≦90 withx+y+z=100%.
 10. The adhesive formulation according to claim 9, whereinsaid weight percentages are such that 30≦x≦89, 1≦y≦30, and 10≦z≦70 withx+y+z=100%.
 11. The adhesive formulation according to claim 1, whereinthe epoxy resin is selected from the group consisting of the diglycidylether of 2,2-bis(4-hydroxyphenyl)propane, the diglycidyl ether ofbis(4-hydroxyphenyl)methane, the diglycidyl ether of tetrabrominated2,2-bis(4-hydroxyphenyl)propane, the triglycidyl ether oftrihydroxyphenylmethane, the triglycidyl ether of paraaminophenol, thetetraglycidyl ether of methlenedianiline, the tetraglycidyl ether oftetraphenylolethane, the polyglycidyl ethers of phenol/formaldehyderesins, the polyglycidyl ethers of cresol/formaldehyde resins,polyepoxidized resins of the epoxyhydantoin or epoxycyanurate type,epoxidized polyoxypropylenes, glycidyl phthalates and cycloaliphaticepoxy resins.
 12. The adhesive formulation according to claim 1, whereinthe latent hardener for the epoxy resin is selected from the groupconsisting of aromatic diamines and dicyandiamide.
 13. The adhesiveformulation according to claim 12, wherein the latent hardener for theepoxy resin i selected from the group consisting ofbis(aminophenyl)sulphones.
 14. The adhesive formulation according toclaim 12, wherein the quantity of said latent hardener represents 1 to30% of the weight of the epoxy resin.
 15. The adhesive formulationaccording to claim 14, wherein said quantity represents 5 to 15% of theweight of the epoxy resin.
 16. The adhesive formulation according toclaim 12, wherein the latent hardener for the epoxy resin is employed incombination with a catalyst selected from the group consisting of Lewisacids and complexes of Lewis acids with amines, ethers or alcohols. 17.The adhesive formulation according to claim 1, wherein the hardener forthe epoxy resin is a compound of the Lewis acid type, said compoundbeing used in a quantity of from 0.5 to 10% by weight of the epoxyresin.
 18. The adhesive formulation according to claim 17, wherein saidquantity of hardener is from 1 to 6% by weight of the epoxy resin. 19.The adhesive formulation according to claim 1, wherein the multiacrylicesters present in the formulation correspond to the formula: ##STR7## inwhich A is an m-valent organic radical containing from 2 to 50 carbonatoms, R is a hydrogen or chlorine atom or a C₁ -C₃ alkyl radial, and mis an integer of from 2 to
 5. 20. The adhesive formulation according toclaim 1, wherein the multacrylic esters present in the formulation arediacrylic esters of the formula: ##STR8## in which R₁ isa hydrogen atomor a methyl radical, n is an integer of from 2 to 4, and p is an integerof from 2 to
 12. 21. The adhesive formulation according to claim 20,wherein n is 2 or
 3. 22. The adhesive formulation according to claim 20,wherein p is from 2 to
 8. 23. The adhesive formulation according toclaim 1, wherein the free-radical generating system consists of at leastone peroxy compound which is soluble in the monomeric acrylic phase andwhose free-radical generating action is inhibited by oxygen, or acombination of said peroxy compound, with at least one activator. 24.The adhesive formulation according to claim 23, wherein the peroxycompound is a hydroperoxide or a compound capable of decomposing orhydrolyzing in situ to give a hydroperoxide.
 25. The adhesiveformulation according to claim 24, wherein the hydroperoixde has theformula R₄ OOH, in which R₄ is C₂ -C₁₈ hydrocarbon radical or a C₁₂ -C₁₈hydrocarbon radical substituted by one or mroe functional groups withoutaction on the hydroperoxide functional group.
 26. The adhesiveformulation according to claim 25, wherein said hydrocarbon radical orsubstituted hydrocarbon radical contains from 3 to 12 carbon atoms. 27.The adhesive formulation according to claim 25, wherein the radical R₄is selected from the group consisting of an alkyl, aryl and aralkylradical.
 28. The adhesive formulation according to claim 23, wherein theoverall quantity of peroxy compounds represents less than 10% of theweight of the monomers to be polymerized which are present in theformulation.
 29. The adhesive formulation according to claim 28, whereinsaid overall quantity is from 0.1 to 6% of said weight.
 30. The adhesiveformulation according to claim 23, wherein the activator used incombination with the peroxy compounds in the free-radical generatingsystem is selected from the group consisting of succinimide,phthalimide, formamide, tertiary amines in which the radicals attachedto the ntirogen contain up to 10 carbon atoms, heterocyclic secondaryamines, organic sulphimides alone or in combination with heterocyclicsecondary amines or N,N-dialkylarylamines.
 31. The adhesive formulationaccording to claim 30, wherein said tertiary amines used in combinationwith the peroxy compounds in the free-radical generating system aretrialkylamines or dialkylarylamines.
 32. The adhesive formulationaccording to claim 30, wherein the total quantity of activator is lessthan 10% of the weight of the monomers to be polymerized which arepresent in the formulation.
 33. The adhesive formulation according toclaim 32, wherein said total quantity of activator is from 0.05% to 6%of said weight.
 34. The adhesive formulation according to claim 1,further comprising at least oen additive selected from the groupconsisting of chelating agents for metallic impurities, polymerizationinhibitors, plasticizers, thickeners, colorants and thixotropic agents.35. The adhesive formulation according to claim 1, further comprisingdissolved oxygen.
 36. The adhesive formulation according to claim 1,further comprising a saturating amount of oxygen.
 37. A method ofadhering substrates together comprising administering an effectiveamount of the adhesive formulation of claim 1 to one or both of thesubstrates and bringing the substrates together to form an anaerobicadhesive bond therebetween.